The present invention relates to a receptacle-type optical transmission/reception apparatus used for optical communication and, more particularly, to a reliable apparatus which can be manufactured at a low cost and a method of manufacturing the same.
An optical transmission/reception apparatus (to be referred to as an optical module hereinafter) for transmitting/receiving an optical signal is one of the basic devices that support the optical communication technology. To popularize information service systems including optical fiber cable wiring to end subscribers, each subscriber must be equipped with an inexpensive optical module.
The arrangements and structures of components for optically coupling an optical fiber to a semiconductor laser or photodetector in an optical module require a fixing accuracy on the order of .mu.m. Accordingly, not only cost reduction but also an increase in accuracy and reliability is required for the optical module.
A receptacle-type optical module in which an optical fiber connector is detachable is known as a form of optical modules. The receptacle-type optical module does not require mounting a pigtail fiber, unlike a device with a pigtail fiber, and is advantageous in cost reduction. For this reason, the receptacle-type optical module has received a great deal of attention in recent years and is commercially available. Such a receptacle-type optical module is described in, e.g., "IEICE Papers" 94, Vol. J77-C-1, No. 11, pp. 695-702, or Jpn. Pat. Appln. KOKAI Publication No. 7-198999.
The conventional receptacle-type optical module is a device dedicated to either transmission or reception.
For the conventional receptacle-type optical module, the ferrule of an optical fiber connector is mounted in the receptacle of the receptacle-type optical module, and thereafter, optical components including a semiconductor laser device are fixed in the optical module.
However, such positioning cannot help being difficult. Without knowing the direction and magnitude of a positional shift from the optical axis of the optical fiber, the semiconductor laser device must be positioned, i.e., the accurate position of the semiconductor laser device must be found out along the optical axis and in a direction perpendicular to the optical axis with trial and error. This operation takes, a long time and much labor until positions where the components are fixed are determined. This problem in manufacturing is one of factors preventing cost reduction.
In the optical modules disclosed in the prior art, a glass plate provided in the receptacle of the receptacle-type optical module is used in order to contact tightly with the ferrule of the optical fiber connector. This structure intends to prevent light emitted from the semiconductor laser device from being reflected by the optical fiber end face and returning to the laser device. Such reflected/returning light makes the operation of the semiconductor laser device unstable and, consequently, adversely affects the transmission characteristics, e.g., increases noise in emitted light.
However, even when a proper physical contact is obtained between the glass plate and the optical fiber ferrule, reflected light from the optical fiber end face still exists provided the refractive index of the glass plate and that of the optical fiber are not the same. And the reflected light returns to the semiconductor laser device. The above problem has not been solved yet.